This invention relates to magnetic reproducing systems, in which a magnetic head is moved relative to and along a magnetic recording track formed in a magnetic recording medium for obtaining a reproduced signal.
In the prior art magnetic reproducing system, the magnetic recording tape is arranged such that its magnetic coating layer 2 formed on a base 1 is moved past the front of a ring type magnetic head 3 as shown in FIG. 1. The magnetic head 3 has a coil 4 wound on its core, and as the magnetic tape is run past the front of the head 3, a voltage is induced as a reproduced signal across the coil 4 in accordance with the changes of the magnetic field formed in the magnetic layer 2. With the prior art reproducing system of this kind, sufficiently great magnetic flux is required for obtaining sufficient reproduced output with a satisfactory signal-to-noise ratio. Therefore, it has been necessary to make the width of the recording track formed on the magnetic tape to be greater than a predetermined value. FIG. 2 is a graph showing the relation between the signal-to-noise ratio of the reproduced output and the track width W in the prior art reproducing system. As is seen from the Figure, where the track width is above 50 microns, the relation of the signal-to-noise ratio to the track width is 3 dB/octave, that is, with the doubling of the track width, for instance from 100 microns to 200 microns, the signal-to-noise ratio is improved by 3 dB. Where the track width is 50 microns, the reproducing amplifier noise N.sub.O and tape noise N.sub.T are substantially the same. Where the track width is less than 50 microns, the relation of the signal-to-noise ratio to the track width is 6 dB/octave, and the signal-to-noise ratio is thus suddenly reduced. In this case, the reproducing amplifier noise N.sub.O is greater than the tape noise N.sub.T. The signal-to-noise ratio is related to N.sub.O and N.sub.T as ##EQU1##
In order to increase the reproducing output without increasing the track width W in the above prior art reproducing system of FIG. 1, it has been proposed to increase the number of turns of the coil 4 of the head 3. This method, however, leads to increase of the impedance of the reproducing head as well. This impedance and the reproducing amplifier noise N.sub.O are proportional to each other, and therefore signal-to-noise ratio is not improved so much by the aforementioned method. At present, the optimum combination of the values of the track width W and signal-to-noise ratio available is only 20 microns and 43 dB in spite of the demand for narrower track widths in the video tape recorders and magnetic discs in order to obtain long period recording and reproduction. With the prior art reproducing system, therefore, reproduced output of a signal-to-noise ratio of about 43 dB could not have been obtained with a track width of less than 20 microns.